The present invention relates to a vehicle air conditioning apparatus including a variable displacement type compressor, an oil separator and a control valve that controls displacement of the compressor based on differential pressure between two pressure monitoring points set in a refrigerant circulation circuit.
Japanese Unexamined Patent Publication No. 2001-107854 discloses this type of air conditioning apparatus.
Specifically, the air conditioning apparatus includes a variable displacement type compressor (hereinafter referred to a compressor) and a control valve that controls displacement of the compressor based on differential pressure between two pressure monitoring points set in a refrigerant circulation circuit. Also, a fixed throttle is placed between the two pressure monitoring points.
The control valve includes a pressure sensing member that is displaced in accordance with variation of the differential pressure between the two pressure monitoring points. Thereby, a valve body of the control valve is operated so as to cancel the variation of the differential pressure. Thus, displacement of the compressor is controlled. When refrigerant gas passes through the fixed throttle, pressure loss of the refrigerant gas is caused by the fixed throttle. Thus, the fixed throttle manifests the differential pressure between the two pressure monitoring points. That is, the fixed throttle serves as means for manifesting the differential pressure. Thereby, the control valve is easily controlled in accordance with the differential pressure. Thus, displacement controllability of the control valve is improved.
If an oil separator is provided with the prior art air conditioning apparatus, pressure loss of the refrigerant gas is caused not only by the oil separator but also by the fixed throttle. The oil separator conventionally separates oil contained in the refrigerant gas from the refrigerant gas and returns to the compressor. Thereby, the internal parts of the compressor are sufficiently lubricated. In addition, the oil that adheres to the inner wall of a heat exchanger constituting the refrigerant circulation circuit is reduced, and efficiency for exchanging heat is raised. Thereby, volumetric efficiency of the compressor is improved. The heat exchanger includes an evaporator and a condenser. However, deterioration of the volumetric efficiency of the compressor caused by the pressure loss of the refrigerant gas exceeds effect of the improvement of the volumetric efficiency caused by the oil separator. Consequently, the volumetric efficiency of the compressor as a whole deteriorates.